As electronic technologies continue to develop, the need for precise, robust, and easily tunable pulse width modulation power supplies also increases. This need is felt in virtually any area of technology that requires precise control over the pulse width emitted from a power supply. It is needed, by way of example, in technologies ranging from the power supplies in personal computers and other consumer electronics, to the high power demands of plasma generating technologies used in chip manufacturing.
For example, there exists in the chip manufacturing field a need for such a precise, robust, and easily tunable pulse width modulation power supply control. As chip manufacturing technologies develop, the capability to increase the number of elements on a semiconductor chip also increases. It is beneficial to increase the number of elements on a semiconductor because as the element density on the semiconductor chips increase, the capabilities of the chip also increases. For example, with higher densities, a chip may perform a greater number of operations in a given clock cycle.
In order to manufacture a chip, the pathways, interconnections, and elements must be etched on a substrate. This etching process is most commonly accomplished in a plasma chamber. During the etching process, the input power to the plasma chamber is switched on and off according to the patterns and the interconnections being etched on the substrate. As would be expected, as the desired chip density increases, the level of control and precision required of the input power to the plasma chamber during the etching process also increases. The smaller and closer together elements on the chip are, the smaller the duration of the “on” and “off” periods of the power supply may be.
Accordingly, in order for the plasma chamber to properly etch a high-density substrate, it must be capable of regulating the applied power to the plasma chamber quickly and precisely. The power supply to the plasma chamber must thus be capable of fine control of output power.
Present control circuitry for power supplies are, however, incapable of providing sufficient pulse width resolution. One reason is that their control circuitry simply runs at an insufficiently high clock frequency.
Accordingly, one attempt to overcome this deficiency in present power supplies has been to use control chips within the power supply that are capable of responding to higher clock frequencies, and to drive these chips with a higher clock frequency.
For example, the use of discrete ECL logic chips driven by a one gigahertz oscillator would provide a very quick reaction time in the power supply, which would allow the power supply to provide very short time intervals and durations of power input to the plasma chamber. This method, however, has several drawbacks. First, the required circuitry is relatively large and therefore occupies valuable space on the circuit board. Second, the higher clock frequency required consumes a large amount of power. Therefore, the circuit can become expensive to operate due to the larger power requirements, and may require additional cooling, due to increased heat generation. Lastly, the higher frequency components themselves can be very expensive.
Another attempt to overcome the above deficiencies has been to use analog control circuitry rather than higher frequency digital circuitry. By using analog circuitry to control the switching of the power supply, many of the above disadvantages are remedied. The circuitry itself is comparatively inexpensive. Moreover, due to its asynchronous design, it is capable of reacting very quickly. However, the use of analog circuitry introduces several other drawbacks. Analog circuitry can be very sensitive, and is very often affected by electrical noise, especially in high power applications. This causes what is known as “waveform jitter.” This phenomenon causes distortion in the power waveform, which results in a loss of precision in the control of the power supply. Furthermore, not only does the waveform jitter phenomenon cause a loss of precision in controlling the switching of the power supply, it also causes a loss of repeatability in the output from the plasma generator. Accordingly, analog circuitry that is susceptible to this waveform jitter makes it an unacceptable alternative phenomenon in high-density chip fabrication, which requires very precise control of the power supply.
Similarly, there also exists a need in the area of consumer electronics for such a precise, robust and easily tunable pulse width modulation power supply. Power systems typically used in personal computers are often placed under rigorous demands. For example, a power supply in a computer may be required to supply different voltages within a very short amount of time. This may occur when a computer switches from “sleep” or “standby” mode to “active” mode. In this situation, a power system in a personal computer typically will have to change the load current at a rate that may exceed 30 amps per microsecond. Such requirements are typically satisfied by a fast response DC/DC converter located very close to the microprocessor. Similarly, many DC/DC converters, for example, the Voltage Regulator Module (VRM) for many microprocessors manufactured by Intel, require the output voltage from a power supply to be digitally programmable.
Typically, these problems have been addressed through the use of analog circuitry. However, for the reasons discussed above, the use of analog circuitry is often unsatisfactory. Similarly, as discussed above, the use of purely digital circuitry is also often an unacceptable alternative due to the prohibitive cost. Accordingly, there exists a need for a low cost, high precision solution.